[MarioCadenas]

Summary

Add Unity AI Gateway (Unity Gateway V3) model services as an app resource type, and let the agents plugin use one as its default model. The backend models a model service as the existing uc_securable app resource with securable_type: MODEL_SERVICE and a single EXECUTE permission, behind the enableModelServiceAsAppsResource SAFE flag (universe PRs 2571640, 2571642, 2571645, 2586620, 2589111).

Changes

• Register model_service as a resource type: manifest schema, permission schema (EXECUTE only), DABs binding table, plugin-create defaults, generated registry types, and the generated JSON schemas.
• Agents plugin: add an optional agents-model-service resource (field name, env DATABRICKS_MODEL_SERVICE_NAME, EXECUTE). The existing agents-serving-endpoint resource is unchanged.
• Default model resolution: defaultModel config, then DATABRICKS_MODEL_SERVICE_NAME, then DATABRICKS_SERVING_ENDPOINT_NAME. The no-model error names both env vars.
• Routing in adapterFromModelString: any dotted name (catalog.schema.name, including system.*) goes to the AI Gateway; names without dots stay on Model Serving. Serving-endpoint names cannot contain dots, so no existing endpoint changes routing.
• knip.json: pnpm knip (run by the pre-commit hook) fails on a clean main (unused packages/appkit/bin/appkit.js, unused devDependencies esbuild, ora, zod), so no commit passes the hook from a fresh checkout. This PR adds those to knip.json so the hook passes; it can be split out if preferred.

Contract (shared with the Databricks CLI PR databricks/cli#6998)

• Type model_service, field name = model service full UC name (catalog.schema.model_service, without the model-services/ prefix).
• Permission EXECUTE. Service principal only (no user API scope).
• DABs binding: { "yamlKey": "uc_securable", "varFields": [["name", "securable_full_name"]], "staticFields": [["securable_type", "MODEL_SERVICE"]] }.

Tests

• packages/appkit/src/agents/tests/databricks.test.ts: dotted user model service name routes to the AI Gateway; system.* still does; plain endpoint names route to Model Serving.
• packages/shared/src/schemas/manifest.test.ts: model_service accepts EXECUTE and rejects other permissions; binding is uc_securable / MODEL_SERVICE; not OBO-capable and not app-only.
• packages/appkit/src/plugins/agents/tests/default-model.test.ts: DATABRICKS_MODEL_SERVICE_NAME wins over DATABRICKS_SERVING_ENDPOINT_NAME; serving endpoint env still used alone; defaultModel wins over both; the error names both env vars. Removing the model service fallback makes the precedence test fail.
• Locally: vitest run (5779 passed, 1 skipped), pnpm typecheck, pnpm check, pnpm knip, and generate:types with no diff in the checked generated files.

Not done / assumptions

• No doctor existence probe for model_service: the JS SDK used by AppKit has no model service API.
• The routing change assumes the AI Gateway accepts a user model service by its full UC name in the request body, like system.* models. Not verified end to end.

This pull request and its description were written by Isaac.

[github-actions]

📦 Bundle size report

Compared against bundle-size-baseline.json (main).

@databricks/appkit

npm tarball (packed): 1.2 MB (+388 B) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	1.2 MB (+835 B)	447 KB (+180 B)
Type declarations	459 KB (+3.3 KB)	165 KB (+74 B)
Source maps	2.5 MB (+1.2 KB)	837 KB (+173 B)
Other	11 KB	3.7 KB
Total	4.1 MB (+5.3 KB)	1.4 MB (+427 B)

Per-entry composition (own code — deps external (as shipped))

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
.	102 KB (+54 B)	2.5 KB (+1 B)	105 KB (+55 B)	external	332 KB (+237 B)
./beta	99 KB (+146 B)	484 B	99 KB (+146 B)	external	298 KB (+664 B)
./testing	42 KB (+76 B)	32 KB (-2 B)	74 KB (+74 B)	external	215 KB (+235 B)
./tsdown	520 B	0 B	520 B	external	813 B
./type-generator	23 KB	0 B	23 KB	external	66 KB

Chunks:

Entry	Chunk	Load	Size (gz)
.	index.js	initial	97 KB
.	utils.js	initial	4.6 KB
.	remote-tunnel-manager.js	lazy	2.5 KB
./beta	beta.js	initial	81 KB
./beta	stream-manager.js	initial	5.9 KB
./beta	service-context.js	initial	4.2 KB
./beta	databricks.js	initial	3.3 KB
./beta	wide-event-emitter.js	initial	3.2 KB
./beta	client.js	initial	594 B
./beta	index.js	initial	20 B
./beta	supervisor-api.js	lazy	192 B
./beta	databricks.js	lazy	177 B
./beta	index.js	lazy	115 B
./testing	manifest.js	initial	29 KB
./testing	index.js	initial	10 KB
./testing	wide-event-emitter.js	initial	2.9 KB
./testing	index.js	lazy	28 KB
./testing	remote-tunnel-manager.js	lazy	2.5 KB
./testing	utils.js	lazy	1.8 KB
./tsdown	index.js	initial	520 B
./type-generator	index.js	initial	23 KB

@databricks/appkit-ui

npm tarball (packed): 397 KB (+4 B) — gzipped download (dist + bin; excludes release-only docs/NOTICE).

dist	raw	gzip
JS (runtime)	428 KB	146 KB
Type declarations	266 KB	98 KB (+1 B)
Source maps	852 KB	285 KB
CSS	16 KB	3.2 KB
Total	1.5 MB	533 KB (+1 B)

Per-entry composition (consumer bundle — deps bundled, peerDeps external)

Entry	Initial (gz)	Lazy (gz)	Total (gz)	node_modules (min)	Own code (min)
./js	5.3 KB	49 KB	55 KB	208 KB	14 KB
./js/beta	2.1 KB	0 B	2.1 KB	0 B	5.0 KB
./react	433 KB	49 KB	481 KB	1.3 MB	177 KB
./react/beta	4.9 KB	0 B	4.9 KB	0 B	12 KB

Chunks:

Entry	Chunk	Load	Size (gz)
./js	index.js	initial	5.2 KB
./js	chunk	initial	120 B
./js	apache-arrow	lazy	49 KB
./js/beta	beta.js	initial	2.1 KB
./react	index.js	initial	431 KB
./react	tslib	initial	2.1 KB
./react	apache-arrow	lazy	49 KB
./react/beta	beta.js	initial	4.9 KB

[github-actions]

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📦 Try this PR's app template

Scaffolds a new app from this PR's SDK build. Run it in any folder (requires the GitHub CLI — gh auth login — and the Databricks CLI):

gh run download 37909750859 -R databricks/appkit -n appkit-template-0.87.0-pr.66c5199-feat-model-service-resource-649 -D appkit-pr-649 \
  && unzip -o "appkit-pr-649/appkit-template-0.87.0-pr.66c5199-feat-model-service-resource-649.zip" -d "appkit-pr-649" \
  && databricks apps init --template "appkit-pr-649"

The template pins @databricks/appkit and @databricks/appkit-ui to tarballs built from this branch, so the scaffolded app runs against this PR's code.

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